The processing of nociceptive information in the spinal dorsal horn may change significantlyfollowing peripheral nerve injury or inflammation to ultimately lead to the development of persistent pain. We previously established that loose ligation of the sciatic nerve was closely associated with (1) activity- dependent long-lasting synaptic plasticity and (2) the activation of cyclic AMP response element binding protein (CREB). CREB activation alters the expression of many genes, including those coding for the post- synaptic density (PSD) proteins Homer and Shank. The Homerla, Ib and Ic and Shankl and 2 isoforms may play important roles in the activity-dependent remodeling of the PSD that ultimately leads to increased synaptic efficacy. In the present application we will investigate the relationship between loose ligation of the sciatic nerve and these Homer and Shank isoforms. Our central hypothesis is that sciatic ligation-associated regulation of Homerla, Ib and Ic and Shankl &2 gene expression promotes the remodeling of the post- synaptic density (PSD) in spinal dorsal horn neurons. We surmise that this remodeling critically contributes to the long-lasting increases in synaptic efficacy that eventually lead to neuropathic pain, hi Specific Aim 1 we will examine if selected pre-transcriptional mediators 'translate'the sciatic ligation into changes in Homer and Shank gene expression, hi Specific Aim 2 we will employ specific small interfering RNAs in an attempt to 'silence'Homer and Shank gene expression and establish whether this modifies their protein levels and distribution in the PSD of spinal dorsal horn neurons within hours of the sciatic ligation. In Specific Aim 3 we seek to establish if manipulations of Homer and Shank gene expression and protein levels alter mechanical allodynia and thermal hyperalgesia as behavioral signs of neuropathic pain several days after the sciatic ligation. We strive to achieve two main goals in this proposal. First, from a cellular perspective we wish to delineate the consequences of injury-elicited primary afferent activity on the PSD structure in the spinal dorsal horn. Second, from a therapeutic perspective, we seek to achieve better target specificity. The remodeled PSD may be a common reflection of injury-elicited changes in several receptors, pathways, transcription factors and genes. If our experiments suggest that regulation of Homer and Shank gene expression plays an important role in the remodeling of the 'pain'PSD then our successful completion of this proposal should provide a solid basis for future therapeutic interventions.